ProSoundWeb Community

Please login or register.

Login with username, password and session length
Advanced search  

Pages: 1 ... 6 7 [8] 9 10 ... 55   Go Down

Author Topic: brain storm an optimal human safety system for back line  (Read 95684 times)

Stephen Swaffer

  • Hero Member
  • *****
  • Offline Offline
  • Posts: 2177
Re: brain storm an optimal human safety system for back line
« Reply #70 on: December 27, 2014, 06:36:28 pm »

Why do the grounds need to be isolated?  In a correctly wired system, they will be bonded together at some point anyway?
Logged
Steve Swaffer

John Roberts {JR}

  • Hero Member
  • *****
  • Offline Offline
  • Posts: 16272
  • Hickory, Mississippi, USA
    • Resotune
Re: brain storm an optimal human safety system for back line
« Reply #71 on: December 27, 2014, 08:10:33 pm »

Why do the grounds need to be isolated?  In a correctly wired system, they will be bonded together at some point anyway?
In theory they could be hard connected but guitar amps are high gain and single ended so likely to hum if the grounds are corrupted... the mic input ground is common mode to the 2 differential mic inputs so should be less likely to pick up noise, but also has a lot of gain so isolated is better IMO.

I believe floating the two grounds with 4 diodes between them is probably a good idea because sundry grounds from different power drops could easily have measurable voltage between them.

JR
Logged
Listen to what a properly "cleared" drum sounds like.   http://circularscience.com/

Mike Sokol

  • Moderator
  • Hero Member
  • *****
  • Offline Offline
  • Posts: 3351
  • Lead instructor for the No~Shock~Zone
    • No~Shock~Zone Electrical Safety
Re: brain storm an optimal human safety system for back line
« Reply #72 on: December 27, 2014, 09:27:00 pm »

Why do the grounds need to be isolated?  In a correctly wired system, they will be bonded together at some point anyway?

Most non-isolated grounds will measure anywhere from 0.1 volts up to 2 volts difference between different outlets on opposite sides of a room, or coming from different panels. And this ground voltage differential can change when the loads shift in a building, such as lighting and heaters. Heck, I've even heard refrigerator compressors and big coffee urns modulate ground loop hum when they kick in. If you want to see/hear something crazy, then think about what can happen with standard bootleg grounds or swapped ground/neutral lines. Those conditions will allow the ground voltage differentials to jump up and down by 5 volts or more, depending on load.

The real challenge is that there's a lot of installed power distro that was never grounded properly in the first place, and this shock prevention system needs to account for all sorts of wiring errors.
« Last Edit: December 27, 2014, 09:31:34 pm by Mike Sokol »
Logged
Mike Sokol
mike@noshockzone.org
www.NoShockZone.org

John Roberts {JR}

  • Hero Member
  • *****
  • Offline Offline
  • Posts: 16272
  • Hickory, Mississippi, USA
    • Resotune
Re: brain storm an optimal human safety system for back line
« Reply #73 on: December 27, 2014, 10:23:47 pm »

Most non-isolated grounds will measure anywhere from 0.1 volts up to 2 volts difference between different outlets on opposite sides of a room, or coming from different panels. And this ground voltage differential can change when the loads shift in a building, such as lighting and heaters. Heck, I've even heard refrigerator compressors and big coffee urns modulate ground loop hum when they kick in. If you want to see/hear something crazy, then think about what can happen with standard bootleg grounds or swapped ground/neutral lines. Those conditions will allow the ground voltage differentials to jump up and down by 5 volts or more, depending on load.

The real challenge is that there's a lot of installed power distro that was never grounded properly in the first place, and this shock prevention system needs to account for all sorts of wiring errors.

I was pulling the 4 diode drops (roughly 2.4V peak) out of thin air... do you think I need to go to 3x or 4x bridges (4.8V) to be safe? I don't want to conduct current between safety grounds unless there is a hazardous fault, to keep the audio clean.

For human safety 5V is nothing, and as soon as the diodes heat up and melt they fail as dead shorts anyhow...

JR
Logged
Listen to what a properly "cleared" drum sounds like.   http://circularscience.com/

Lyle Williams

  • Hero Member
  • *****
  • Offline Offline
  • Posts: 1546
Re: brain storm an optimal human safety system for back line
« Reply #74 on: December 28, 2014, 03:52:16 am »

The real challenge is that there's a lot of installed power distro that was never grounded properly in the first place, and this shock prevention system needs to account for all sorts of wiring errors.

How does this new system differ from the current wiring rules which need to account for all sorts of wiring errors?

Is it a device we are looking for, or just a practice?  Ie, do all racks get tied together with 4AWG earthing cables before any power is applied?

Logged

John Roberts {JR}

  • Hero Member
  • *****
  • Offline Offline
  • Posts: 16272
  • Hickory, Mississippi, USA
    • Resotune
Re: brain storm an optimal human safety system for back line
« Reply #75 on: December 28, 2014, 11:20:02 am »

How does this new system differ from the current wiring rules which need to account for all sorts of wiring errors?

Is it a device we are looking for, or just a practice?  Ie, do all racks get tied together with 4AWG earthing cables before any power is applied?

If everything was wired properly and working properly there would be no need for UL or safety rules.

I am trying to protect against multiple hazards.

#1 guitar amps going rouge either from bad stinger cap or other fault with ungrounded chassis.
#2 reverse bootleg mis-wired outlets (at FOH or Back line).
#3 open neutral at FOH or Backline

My shunt between the two safety grounds is not intended to be a fix, but to cause the offending device to take out it's power breaker or GFCI. Hopefully the people involved will consider this as more than a nuisance trip and a real life safety hazard.

I was thinking instead of a LED putting an audible alarm inside the safety shunt to make an annoying sound when fault currents are flowing between safety grounds.

JR
Logged
Listen to what a properly "cleared" drum sounds like.   http://circularscience.com/

Stephen Swaffer

  • Hero Member
  • *****
  • Offline Offline
  • Posts: 2177
Re: brain storm an optimal human safety system for back line
« Reply #76 on: December 28, 2014, 03:11:33 pm »

Keep in mind that tripping the circuit breaker will require significantly more than 20 amps to do so quickly-most breakers are inverse time delay.  The circuit resistance (an unknown) plus diodes will limit the current to some degree-the greater the limiting the longer it will take to trip the breaker-and some brands of breakers are notorious for taking extended time to trip.

While dual current sensors plus a relays IS more complex, it is less dependent on external factors, IMO.

Mike is right-getting people to view any shock as unacceptable is the key-then they will look for a solution be it a NCVT or whatever.  The next hurdle will be to get them to view an occasional GFCI trip as less of a nuisance than an occasional shock.
Logged
Steve Swaffer

John Roberts {JR}

  • Hero Member
  • *****
  • Offline Offline
  • Posts: 16272
  • Hickory, Mississippi, USA
    • Resotune
Re: brain storm an optimal human safety system for back line
« Reply #77 on: December 28, 2014, 05:09:01 pm »

Keep in mind that tripping the circuit breaker will require significantly more than 20 amps to do so quickly-most breakers are inverse time delay.  The circuit resistance (an unknown) plus diodes will limit the current to some degree-the greater the limiting the longer it will take to trip the breaker-and some brands of breakers are notorious for taking extended time to trip.
I know... the ground bonding test used by UL was around 50A for maybe ten seconds, something like that it was a couple decades ago.

I suspect the combination of mic cord ground resistance and guitar cable resistance could be an ohm or two, but that should still trip a breaker. If it doesn't we have more problems. I would not be surprised if we also see the cords get so hot they melt insulation and deform.
Quote

While dual current sensors plus a relays IS more complex, it is less dependent on external factors, IMO.
Perhaps we can approach this on multiple tracks. For cost is no object,  I would drop in an isolated power supply ($10-20), circuitry to sense current ($15-20), and open not only a relay for the signal and a relay for all three power circuits (another $10?). then this needs to get built into a slick package, for sale to all three or four potential customers.   

The low cost shunt seems more affordable by a larger number of musicians.

Quote

Mike is right-getting people to view any shock as unacceptable is the key-then they will look for a solution be it a NCVT or whatever.  The next hurdle will be to get them to view an occasional GFCI trip as less of a nuisance than an occasional shock.

I have found in life that educating and convincing people to do what they should is a lot harder than providing solutions that do not require them to learn new stuff, or change their former behavior. 

JR

Logged
Listen to what a properly "cleared" drum sounds like.   http://circularscience.com/

Stephen Swaffer

  • Hero Member
  • *****
  • Offline Offline
  • Posts: 2177
Re: brain storm an optimal human safety system for back line
« Reply #78 on: December 28, 2014, 09:07:05 pm »

  
The low cost shunt seems more affordable by a larger number of musicians.


It is not surprising that a more robust, comprehensive solution costs more than a solution that primarily protects against one failure mode-but the value of each is very subjective-and you are more qualified to make that subjective judgement than I am.

As you pointed out the chief down side of the shunt is finding a way to prevent getting shocked while connecting it.  The only two ways I can think of are 1.  Connecting all power connections last, or 2. using a NCVT to verify. I doubt power to the backline and/or FOH will be disconnected during a quick change over-and if you use an NCVT you effectively eliminate the need for the shunt-unless something fails during the performance.

You might consider a Diac shunt for simplicity-if you can find one that would handle the short circuit current, they typically have a threshold of 30 volts.

Of course, another option is to get the pricier option mandated by code for stage use to increase the demand ;D.
Logged
Steve Swaffer

John Roberts {JR}

  • Hero Member
  • *****
  • Offline Offline
  • Posts: 16272
  • Hickory, Mississippi, USA
    • Resotune
Re: brain storm an optimal human safety system for back line
« Reply #79 on: December 28, 2014, 09:45:09 pm »

It is not surprising that a more robust, comprehensive solution costs more than a solution that primarily protects against one failure mode-but the value of each is very subjective-and you are more qualified to make that subjective judgement than I am.
While there may be some debate, in my judgement shunting the two safety grounds together will protect against all of the sundry hazards I enumerated, while it counts on the mains power circuit breakers to trip from over current.
Quote

As you pointed out the chief down side of the shunt is finding a way to prevent getting shocked while connecting it.  The only two ways I can think of are 1.  Connecting all power connections last, or 2. using a NCVT to verify. I doubt power to the backline and/or FOH will be disconnected during a quick change over-and if you use an NCVT you effectively eliminate the need for the shunt-unless something fails during the performance.

Actually a practical way is to add a switch so the two grounds are not shunted until the switch is closed completing the circuit between the two grounds. Of course the cable jockey needs to be careful about touching the mic cable ground and guitar cable ground at the same time. Of course the downside to the shunt having an off switch is that operator may open the switch to reduce hum, if the grounds are more than the several volts apart that the diodes account for, and hum happens. 

Quote
You might consider a Diac shunt for simplicity-if you can find one that would handle the short circuit current, they typically have a threshold of 30 volts.
Think about it, current is not the problem as much as power dissipation. 20A x 30V is 600W. So any diac will quickly turn into a puddle of melted or vaporized silicon. I'll stay with my diode bridges, I have tested them with 120V  across them and they survive taking out a typical fuse/breaker.
Quote
Of course, another option is to get the pricier option mandated by code for stage use to increase the demand ;D.
no... that would be government over reach... while I wouldn't mind GFCI in bar outlets.

I may be imagining a problem that isn't really serious. If more musicians were killed, we might see more electrical building inspectors that know what they are doing to prevent problems. The last one we heard about was in Argentina and not to stereotype, but who knows what kind of electrical inspections they have.

A possible market for a high end box is for the money channel... Big name talent can afford the insurance for not getting zapped while using their favorite gear... While how many of them are still on wired mics?

So chicken egg... the guys who can afford it don't need it, and the guys who need it can't (won't) pay for it.

Still an interesting mental exercise.

JR
Logged
Listen to what a properly "cleared" drum sounds like.   http://circularscience.com/
Pages: 1 ... 6 7 [8] 9 10 ... 55   Go Up
 


Page created in 0.039 seconds with 24 queries.